If you have already completed this, or want to look at different rounds, below is a list of the different rounds which currently have walkthroughs:
This is a walkthrough for rounds 41-50 of Bloons Tower Defense 5 on Easy. If you haven't already done so, buy the Supermonkey which you should have just unlocked.
Begin round 41, and watch as your amazingly good tower defense team does the rest of the work, taking out the bloons on the track. This round should present no challenges, just a lot of zebra bloons that are controllable, but will also help cash in a huge sum of money at the end of the level. You should unlock laser vision for your Supermonkey at the end of the level, so go ahead and equip it. For round 42, you must beware as there are many camo bloons. In order to sneak past this level, use road spikes. Place about ten at the end of the level to stop the camo bloons reaching the end.
The next round should be a reasonably easy breeze, but more of the bloons are starting to get through, so it is time to upgrade your Glue Gunner. Choose the Bloon Dissolver, which should be around $2800. Proceed onto the next round, and watch the bloons go down, which they will do quite easily. You will unlock Monkey Apprentices at the end of this round. These are ok, but are also overrated to a certain extent. Save your money, and pass on buying these for now.
With your current setup of defense towers, you should be able to reach the end of round 45 without any pains or troubles from the bloons. At the end of round 45, you will unlock Super Range. Go ahead and buy it. It will increase the range of your Supermonkey by quite a huge amount. At the next round, M.O.A.B maulers will be introduced. These are overlarge bloons, which carry a huge number of bloons in them. Although all will look perilous, you will end up being all good, and the Supermonkey will save you at the last second.
Proceed onto the next round, and equip some Road Spikes, ready for the mass number of camo bloons at the end of the level. Use as little of these as required, and you will have completed round 47. Start round 48, and buy a second Supermonkey. Your defense will be able to complete the round, and at the end, you will get a Monkey Village. Since we are so close to the end, it is not worth investing in them at the current time. Upgrade your second Supermonkey to laser level, and start the round. At the end of the round, you will get quite a few upgrades, including the most important one, Plasma Vision for your Supermonkey. Buy this immediately. Start the final round, and equip some Road Spikes (just in case). A M.O.A.B moaler will present itself, but will be taken down by the Supermonkey you just upgraded easily. You will eventually complete the level, and a message will come up, congratulating you for completing the game on easy! Good job.